Coated wood products are used in the furniture, kitchen cabinet, flooring, and fenestration industries, among others. The coating may include paint, primer, stain, lacquer, varnish, or other such materials. Coatings are applied to wood for aesthetic reasons, surface smoothness, as well as protective barriers to prevent excessive moisture from reaching the wood substrate and accelerating decay.
Surface smoothness is an important feature of many wood products, in particular furniture and building components such as interior trim for windows and doors. Many wood surfaces are not naturally smooth, however. Wood surfaces may have textured structures due to the natural grain of the wood, as well as voids, such as imperfections including cracks, resin channels, knots, worm holes, and mechanical damage. Many voids can be remedied by coating the surface with a layer of polymeric material of sufficient thickness to level out many of the voids, including, for example, cracks. For example, because veneers are relatively thin, any cracks tend to be shallow, and thus fillable by a variety of known coating processes. In some instances, a process of coating, followed by sanding or other mechanical smoothing, may be effective in producing a smooth surface. In the case of some woods, in particular softwoods such as the conifers, the imperfections can take the form of deeper cracks and other voids that are not easily filled using conventional coating processes, due, for example, to the viscosity of the coating fluid, the narrow opening and shape of the crack, and possibly to trapped air in the voids.
Defects resulting from natural variation in the wood substrate as well as conditioning of the wood substrate result in significant scrap, aesthetic deficiencies, or costly labor, materials, and processes to repair those substrates. It is a known aspect of wood, that upon milling and fabrication of components for windows, doors, cabinets, or other products, checks, splits, or other defects may become apparent. No upstream process for solid wood substrate can eliminate the tendency for these naturally occurring aesthetic defects.
If noticed, these defects could be repaired, screened out, or tracked. If unnoticed, these defects (i.e., imperfections) might be covered by conventional coating processes, such as priming and topcoat application. Or, more commonly, these unnoticed defects become more pronounced after priming and topcoat application due to the inability of most coatings to bridge large checks/splits by conventional spray coating methods. In these cases, where the defects become more pronounced, a rework step may be needed to sand down the coated part, manually apply some filler putty to the check/split, and recoat the part with primer and topcoat. Or, the alternative may be to scrap the part due to the aesthetic and performance defect.
In the fenestration industry alone, the quantity of scrap wood and labor culling out such scrap can be quite significant. Because the imperfections are typically not noticed until after the wood is coated with a finish, such wood cannot be readily recycled. It is typically placed in landfills. Just in the fenestration industry, as much as 20% of the cut and trimmed components are wasted due to such imperfections.
Ignoring such defects is not acceptable in the manufacture of fenestration units. Upon building a door or window with a defect-containing component, that component would likely absorb more moisture than a component without a defect and promote more rapid decay. Also, the presence of wood substrate defects is increasing due to old wood depletion in the world market. New wood is more prone to developing imperfections such as checks and splits.
One method to preemptively repair wood substrate defects is to wrap the wood component with a veneer, plastic film, composite paper, or other material. The wrap material may be adhered to the wood substrate with adhesive. The film may cover defects such as checks/splits and prevent new defects from occurring by hiding the substrate. This protection comes at a high cost, as wrapping films can be expensive and each wrapping process must be tuned precisely to each component's geometry.
Thus, there is a need for an alternative method for preemptively repairing wood imperfections without costly wraps or manual labor or quality screening to identify defective parts.